One really common solution to slow, and unreliable playback of DVD is the settings related to DMA which is turn "off" by default.

DMA stands for: Direct Memory Access. DMA allows a piece of hardware to talk directly with the RAM, reading and/or writing independent of the CPU (Central Processing Unit). In other words the hardware can use the system memory, bypassing the CPU, allowing the device to read and write much faster.

By default Ubuntu has DMA turned off (set to 0), this can be changed in the /etc/hdparm.conf file, like so:

1. First make a backup of your hdpram file:

# sudo cp /etc/hdparm.conf /etc/hdparm.conf.original

2. Now edit the file using your favorite text editor, I'm using vi, however you can use the editor of you choice: